The R-CQICH (Reverse-Channel Quality Indicator Channel) is a newly added channel for the CDMA-2000 Release C Standard. In such systems, each mobile station operating within the coverage area of a given base station will measure the forward link channel quality and send this information back to the base station. This information consists of a full channel quality information transmitted either during the first slot, the first two slots or the first four slots in a frame. For the remainder of the slots in the frame, only a differential update is transmitted. There are typically 16 slots in a frame. For the full measurement, a repetition factor of 1, 2 or 4 is used meaning that exactly the same measurement is transmitted a number of times indicated by the repetition factor.
The R-CQICH is a continuous channel on the reverse link. In addition to conveying channel quality information, it conveys best serving sector information from the Walsh cover used to transmit the information. More specifically, the mobile station will make a channel quality measurement for each base station/sector that it can detect. It then determines the best channel quality of the group of measurements, and transmits, on the R-CQICH, the identity of the base station for which that measurement was made together with the channel quality indicator.
A Walsh code cover is used in transmitting the R-CQICH. Each sector has its own Walsh cover 10. The mobile station identifies the particular sector for which the channel quality is best by using the Walsh code cover of that sector in generating the R-CQICH.
FIG. 1 shows a block diagram of the R-CQICH channel generation structure provided by CDMA-2000 Release C. For full C/I updates, 4 bits per update are fed to a (12,4) block encoder 20 which produces a 12 bit output. The output of this is then fed to sequence repetition block 22 which repeats the sequence 1, 2 or 4 times as indicated above. For full C/I updates, the switch 25 is switched to connect the output of the sequence repetition 22 to the multiplier 26. The output of the sequence repetition 22 is then multiplied with multiplier 26 by the 8-symbol Walsh cover as indicated at 28. The 8-symbol Walsh cover will indicate which sector will transmit to the mobile on the forward link for the next slot. Finally, the output of the multiplier 26 is multiplied by a 16-symbol Walsh cover as indicated at 30. 96 symbols per slot are output by a multiplier 26. For differential C/I updates, the switch 25 is switched to connect the output of the symbol repetition 24 to the multiplier 26. For differential C/I updates, a single CQI symbol is input to symbol repetition function 24. This is in the form of 1 bit per 1.25 millisecond slot. This single bit is then simply repeated 12 times and output to multiplier 26. It can be seen that a given slot is either used to transmit a full C/I update or the differential C/I update.
It is noted that FIG. 1 is specific to CDMA-2000 Release C 1×EV-DV solutions. An analogous channel has been proposed for IS 856 1×EV-DO applications. In this case, rather than calling the channel the R-CQICH, the channel is called the DRC (Data Rate Control) channel. The structure of the DRC channel is very similar to that of the R-CQICH. FIG. 3 is a block diagram of DRC generation for DO applications. In this case, the DRC symbols are data rate control symbols consisting of four bits per slot. These are fed into a bi-orthogonal encoder 80 which produces eight symbols per slot. This goes through a code word repetition block with factor=2 as indicated at 82. This produces 16 symbols per slot. This is multiplied at 84 by the eight symbol Walsh cover of the particular sector being reported. This produces 128 symbols per slot. This is then spread with a w816 cover at 88 to produce a DRC channel having a rate of 1.2288 Mcps. This second Walsh cover is used to indicate the channel is the DRC channel.